Goldfish are easy to care for and fun to watch. But it's essential that you understand which types can live together. Although goldfish are more social than tropical fish, you could have compatibility issues if you place different types of goldfish together.
The types of goldfish include flat-body and egg-shaped, such as fancy goldfish. Egg-shaped goldfish cannot live with flat-body goldfish.
Egg-shaped goldfish are slow swimmers, and many fancies have trouble seeing. Flat-body goldfish will consume all the food before the egg-shaped ones realize you dropped food in the aquarium.
Egg-shaped or fancy goldfish look round like eggs and have decorative, long fins. Some fancies have bulbous heads or eyes, like the celestial bubble-eye and the black moor. Flat-body goldfish have slim, streamlined bodies and swim quickly. They include the common goldfish and comets.
All types of goldfish can survive in an unheated, indoor aquarium.
All goldfish are social. However, flat-body goldfish may bully the egg-shaped fancies if the aquarium is too small and the fish are competing for space and food.